Defrosting system for refrigeration evaporators



June 5, 1956 R. M. HENDERSON 2,748,571

DEFROSTING SYSTEM FOR REFRIGERATION EVAPORATORS Filed April 3, 1952 1 El 22 1 2O 17/ T .v' G 5 39""[llllfl II SB D 12 M H m INVENTOR.

30 Roy M. Henderson FIG.2

To OZQMQ/VA MAW I ATTORNEYS Unite States DEFROSTING SYSTEM FOR REFRIGERATION EVAPORATORS This invention relates to refrigeration apparatus and more particularly to improved means and method for hot gas defrosting.

Hot gas defrosting for refrigeration evaporators is a comparatively old art, but with the advent of extensive use of extra low temperature refrigerators, im proved methods have become necessary.

The improved methods disclosed herein are based on the premise that defrosting of evaporators in low temperature refrigerators should be accomplished during the least possible period of time to avoid excessive warmup of the refrigerated enclosure or chamber. To accomplish this defrosting in the least possible time, the compressor must be supplied with a constant and sufficient supply of evaporated heat laden gas, for transmission to the evaporator which is being defrosted, to keep the compressor adequately loaded, but not overloaded, during the entire defrosting operation. It is therefore a requirement that not only an adequate quantity of evaporated heat laden gas be supplied to the compressor, but such supply should be regulated and controlled as to the amount so that overloading of the compressor does not occur.

It is common practice in hot gas defrosting systems to position heat exchangers or auxiliary evaporators in the refrigerant line, which conveys the refrigerant from the enclosure evaporator to the low side of the compressor, to reevaporate liquid refrigerant which is condensed as a result of such defrosting before it reaches the compressor. This method, of course, prevents the refrigerant from entering the compressor in liquid form which might cause damage to the compressor, but because of variation in evaporator temperature during defrosting, the amount of refrigerant which is condensed varies and the flow of liquid refrigerant from the evaporator to the auxiliary heat exchanger or evaporator is consequently erratic. The result is that the supply of vaporized heat laden gas is uneven and at times insufficient during the defrosting operation. Consequently the defrosting is not as eflicient and rapid as desirable.

It is therefore a primary object of this invention to provide apparatus in association with a refrigeration system which will permit hot gas supplied from the compressor to defrost an evaporator within a refrigerated chamber, and at the same time assure an adequate and regulated quantity of said defrosting gas.

Another object is to provide in association with a refrigeration system an improved hot gas defrosting system wherein the hot gas will be supplied from the refrigerant as a result of the absorption of heat by an auxiliary evaporator outside the refrigerated chamber and will be transmitted to accomplish the defrosting by the compressor of the refrigeration system.

A further object is to associate a hot gas defrosting system with a refrigeration system in the manner referred to and further provide apparatus for by-passing liquid refrigerant condensed as a result of defrosting around the functional components of the refrigeration atent system which are intermediate the low side of the evaporator and the receiver thereof and directly to the said receiver.

Still a further object is to provide in association with a refrigeration system an improved hot gas defrosting system in which an auxiliary evaporator outside the refrigerated chamber is employed to receive liquid refrigerant from the receiver of the refrigeration system, vaporize it, and thereby provide a supply thereof to the compressor of the refrigeration system for transmission to the evaporator to be defrosted.

Another object is to provide an arrangement of refrigeration apparatus in which a secondary evaporator is arranged outside the refrigerated chamber to absorb heat from a supplied fluid to thereby provide heat for establishing a hot gas for defrosting a refrigeration evaporator within the refrigerated chamber and to control the quantity of supplied fluid by a regulating valve responsible to the suction pressure of the secondary evaporator.

Still another object is to provide a refrigeration system with a hot gas defrosting system employing the refrigerant of the refrigeration system means for lay-passing the liquid condensed during defrosting of the refrigeration evaporator directly to the receiver and thereby eliminate any necessity of re-evaporation of said liquid so it can pass through the compressor of the refrigeration system.

A further object is to provide in association with a refrigeration system a hot gas defrosting system in which the liquid refrigerant of the refrigeration system is employed and the hot gas is obtained by means of a secondary evaporator receiving liquid refrigerant directly from the refrigeration receiver, and then so controlled and supplied to the compressor of said refrigeration system that an adequate uninterrupted flow of hot gas will be present.

Still a further object is to provide a hot gas defrosting system for a refrigeration system in which the liquid refrigerant of the refrigeration system is employed to obtain the hot gas, yet the supplying of refrigerant to the evaporator of the refrigeration system will not be detrimentally affected or adversely influenced as a result of defrosting operations.

Yet a further object is to provide a hot gas defrosting system for a refrigeration system in which a secondary heat absorbing evaporator is associated with the compressor of the refrigeration system and employed to produce the hot gas for defrosting, and further wherein control means will be provided to regulate and control the quantity of heat available to the heat absorbing surface of the secondary evaporator, all responsive to the suction pressure of said secondary evaporator with the result that there will be proper regulation and contro of the quantity of heat absorbed during the defrosting operation.

Another object is to produce an improved and simple hot gas defrosting system for a refrigeration system that can be associated with said refrigeration system in an easy and economical manner by employing standard fittings and valves, together with known timing and control devices to obtain the desired periods of the refrigeration cycle and the defrosting operation.

Other objects of my invention will become apparent from the following description taken in connection with the accompanying drawings in which:

Figure 1 is a schematic view showing, by way of example, a conventional low temperature refrigeration system having associated therewith an example of a hot gas defrosting system embodying my invention; and

Figure 2 is a sectional View of a 3-way valve which is an example of a type that can be employed in the 3 association of the defrosting system with the refrigeration system.

Referring to Figure l in detail, a conventional low temperature refrigerating system is shown with which is to be associated a hot gas defrosting system embodying my invention. This low temperature refrigeration sys tem comprises an evaporator E of the coil type forming tne evaporator section of the system (there may be more cvaporators, but only one is shown for simplicity). This evaporator is positioned in a space or chamber to be refrigerated which is indicated by the letters RC. Also forming part of the conventional system is the compressor C, the condenser D and the liquid receiver The receiver is connected to one end of the evaporator by a liquid conduit line L with which is associated the expansion valve It). There is also a suction line S con nected to the low side 11 of the compressor and to the other end of the evaporator. To this suction line clamped the bulb B which controls the expansion valve it) in a well known manner. The high side 32 of the compressor is connected by a conduit 13 with one end of the condenser D, said other end being connected into the receiver R as shown.

With this conventional refrigeration system, the refrigerant in the evaporator absorbs heat from the space RC being cooled because the refrigerant is held under a pressure at which the liquids boiling temperature is below the temperature of the surrounding air or material in the chamber. The heat flowing into the refrigerant causes it to boil and therefore converted into a vapor. This vapor then passes through the suction line to the compressor C Where it will be compressed to a pressure at which the temperature of the refrigerant is somewhat higher than the cooling medium (generally air or water about the condenser D). At the condenser the heat is transferred from the compressor vapor to the cooling medium of the condenser, thereby causing the refrigerant to condense and liquefy. The liquid refrigerant then passes into the receiver R and subsequently through the liquid line L to the evaporator E through the expansion valve. This expansion valve is designed to keep the line as full of refrigerant as possible and prevent any return. in the evaporator the pressure of the refrigerant becomes reduced, where it again boils and thereby extracts more heat from the chamber RC, with the result that it is changed to a vapor.

The defrosting system which I have shown associated 1 the just described conventional low pressure refrigeration system and which embodies my invention consists of a secondary evaporator SE which can be of the coil type. The purpose of this secondary evaporator is to change the refrigerant in liquid form to a heat laden vapor which will be the hot gas for performing the defrosting operation on the evaporator E of the refrigerating system. in order to provide a body of heat so the refrigerant in the secondary evaporator can absorb heat and become vaporized, the secondary evaporator is placed in a tank T to which warm water will be supplied in a controlled manner. The use of water as a source of heat for the secondary evaporator is shown by way of example only as it is to be understood that other sources of heat can be used if desired, such as air or other gases or other liquids.

The tank T has an inlet conduit 14 and an outlet conduit 15. The secondary evaporator is connected to receive liquid refrigerant from the receiver by a conduit 16. The other end of the secondary evaporator is connceted by a conduit 17 with the suction line S of the refrigeration system by way of a 3-way valve V This 3-.vay valve may be of any well known construction and can be either manually or automatically controlled. Preferably, for automatic defrosting, the valve will be automatically controlled by a solenoid which is connected into a time control circuit in a known manner. A form of 3-Way valve which could be employed is shown 4 in Figure 2 by way of example. The valve V will have a normal refrigeration condition which will disconnect the conduit 17 from the suction line and permit the suction line to be open so as to connect the evaporator E with the low pressure side of the compressor.

In the conduit 16 connecting the receiver with the secondary evaporator, there is inserted an expansion valve 3.8 so as to control the flow of liquid to the secondary evaporator. This expansion valve will be under the control of a thermal bulb SB which will be clamped to the conduit 17 leading from the secondary evaporator to the suction line.

It is also desirable in my defrosting system to not only control the supply of liquid to the secondary evaporator from the receiver, but to also control the flow of water or other heat containing material to the secondary evaporator whereby the refrigerant absorbs heat and boils with the result it vaporizes. The control should be proportionate to the quantity of heat required to ex pand the refrigerant and supply a sufficient amount of expanded refrigerant or vapor to properly load the compressor during the defrosting cycle, but not in an amount to cause any overloading of the compressor. I accomplish this control of the water flowing through the tank T by a regulating valve 19 which can be opened and closed in response to what is commonly known as the suction pressure of the secondary evaporator. Suction pressure is the pressure generated by vaporization of the refrigerant. The control valve element of the regulating valve 19 is connected to the line 17 by the tube 20. The regulating valve 19 may be of any known construction and arranged to function so as to move toward the closed position as the evaporator pressure suction increases and to move toward the open condition as the suction pressure decreases.

My improved hot gas defrosting system also includes a second 3-way valve V which is incorporated in the line 32 of the refrigerating system which connects the high pressure side of the compressor with the condenser The valve V can be of the same construction as the valve V an example of which is disclosed in Figure 2. This 3-way valve will have a normal control position so that during operation of the refrigeration system it will not interfere with the connection of the condenser with the high side of the compressor. The other position of the control element of the 3-way valve will be arranged so as to connect the high pressure side of the compressor to the evaporator E in the refrigerated chamber and this is accomplished by a conduit 21 leading from the valve to a T connector 22 in the suction line 5 between the previously referred to valve V and the evaporator E. As already mentioned, the valve V during defrosting will be in a position to cut off the suction line S from the low ressure side of the compressor. Thus, when the valve V is conditioned for defrosting simultaneously with the conditioning of valve V for defrosting, the high pressure side of the compressor will be directly connected with the evaporator E without being connected with the low pressure side. When the valve V is conditioned for defrosting, it will also be conditioned to cut oil the high pressure side of the compressor with the condenser.

in the operation of my defrosting system, it is also necessary to by-pass the expansion valve 19 in the liquid line L between the receiver and the evaporator E so that liquid from the evaporator E can flow directly to the receiver, such liquid coming from the evaporator csulting from the hot gas condensing in the evaporator during the defrosting thereof. This lay-passing of the expansion valve 7.0 is accomplished by a separate conduit 23 leading directly from the evaporator E to the receiver. in this conduit 23 there will be a check valve 24 which will prevent refrigerant from having any reverse flow toward the evaporator during normal operation of the refrigerating system when on a refrigerating cycle.

When the solenoid is de-energized, valve element 26 is held on seat 24 by the spring 29 and there is a direct connection between line S and the compressor. When the solenoid is energized, the valve element is moved to engage seat 25 and then conduit 17 is connected to the compressor.

The 3-way valve V shown by way of example in Figure 2 comprises a casing H in which are two valve seats 25 and 25' with which the valve element 26 can alternately cooperate. The valve element is carried on the end of a plunger shaft 27 which is movable by the solenoid 23. A spring 29 normally biases the valve element onto the seat 25. The casing has a chamber 30 which is continuously connected to the compressor and line S is disconnected. Within the seat 25' is a chamber 31 to which conduit 17 coming from the secondary evaporator SE is connected. Within seat 25 is a chamber 32 to which the suction line S coming from the evaporator E is connected.

The 3-way valve V can be of like construction and it is believed to be obvious how it will be connected to the condenser, compressor and the conduit 21 to obtain the desired control when the solenoid is not energized or is energized.

Operation During refrigeration operation of the refrigerating system the two valves V and V will be in their normal condition, which insures that the suction line S will be connected to the low side of the compressor and the high side of the compressor will be connected to the evaporator E, through the condenser 18, the receiver R and the liquid line L. When defrosting is desired, both valves V and V will be operated. The valve V will be conditioned so as to disconnect the suction line with the compressor and connect the line 17 with the low side of the compressor in the manner indicated by the arrow adjacent the valve V The operation of the valve V will disconnect the high side of the compressor with the condenser and connect said high side with the suction line by way of the line 21, as indicated by the arrow adjacent the valve V Hot gas will now be created by secondary evaporator SE and the compressor will function to force this hot gas to the evaporator E in the refrigerated chamber RC. The result will be that the evaporator B will be defrosted. As heat is transferred from the hot gas to the outside of the evaporator E to melt the frozen moisture thereon, it will become condensed and return to liquid form. This liquid will then be returned to the receiver R by way of the line 23 which by-passes the expansion valve 1b. The hot gas supplied by the secondary evaporator SE is obtained from the liquid receiver R by way of the conduit 16 and the expansion valve 18. When the liquid enters the secondary evaporator through the expansion valve, it will be maintained under a pressure at which it will boil. The temperature of the refrigerant is below the temperature of the water in the tank T. Consequently, the refrigerant in the secondary evaporator will absorb heat from the warm water in the tank, thereby causing the refrigerant to boil and to be converted into a vapor laden with heat which is the hot gas employed to defrost the evaporator E in the refrigeration chamber. The heat laden vapor coming from the secondary evaporator will be carried by its own generated pressure through the line 17 to the compressor. This generated pressure of the vaporized refrigerant is commonly known as suction pressure and will be referred to by that term in the claims.

When heat is absorbed from the water in the container, the water temperature will be reduced and thus the temperature difierence between the boiling refrigerant and the water will be reduced, with the result that the quantity of heat being absorbed will also be reduced and consequently the suction pressure will have a reduction. When the suction pressure is reduced the water regulating valve will be permitted-to open, since this water regulating valve is connected by the line to the conduit 17 in which the vaporized refrigerant is flowing to the compressor. A reduction in the suction pressure Will then open up the valve 19 with the result that warm water can flow more rapidly through the tank T and thus supply additional warm water and a greater amount of heat for absorption by the refrigerant in the secondary evaporator. By proper adjustment of the regulating valve 19 and having it responsive to the suction pressure of the secondary evaporator, the flow of hot gas to the evaporator being defrosted can be properly regulated and controlled with the result that there will be a constant and adequate flow of hot gas to accomplish the defrosting. This control of the hot gas will also be so arranged that there will not be any overloading of the compressor during defrosting. After defrosting is accomplished, the two 3-way valves V and V will again assume their normal condition so the refrigerating cycle can commence.

It will be noted that my hot gas defrosting system is very simple and the secondary evaporator, tank, regulating valve, etc., can be associated with the conventional refrigeration system in a very cheap and easy manner. Standard parts can be employed to connect the defrosting system into the refrigeration system. It is only necessary to provide the 3-way valves, the by-pass return liquid line and the connecting conduits 17 and 21. The secondary evaporator will be connected to the receiver by a line joined into the refrigeration liquid line, or a separate liquid connection to the receiver.

From the particular defrosting system disclosed, it is believed to be obvious that modifications can be made. There is disclosed one heat supply means for the secondary evaporator and control for the amount of heat available to be absorbed. It is, of course, obvious that other heat sources can be employed and the control thereof can be made by means other than a regulating valve under the control of the suction pressure of the secondary evaporator. It is well known that temperature and pressure in low boiling point refrigerants have a close relationship and thus it is possible to control the supply of heat to the secondary evaporator by a regulating valve which will be responsive to temperature changes of the vaporized gas in the secondary evaporator, instead of the disclosed pressure control regulating valve.

It is particularly stressed in connection with my defrosting system that the condenser is completely isolated during defrosting by the operation of the valves V and V which constitute what is generally known in refrigeration engineering as reversing valves, or broadly means operable to effect reverse cycle operation. Any other known means for accomplishing the directing operation can be used. It is not used in any manner during the defrosting, as has been attempted by some prior defrosting systems. It is to be further noted that in my system there is no attempt at re-evaporation of liquid as it returns through a suction line.

Thus, being aware of the possibility of modifications, all within the principles of my invention, it is to be understood that the scope of the invention is not to be limited in any manner except in accordance with the appended claims.

What is claimed is:

1. In combination with a refrigeration system having a compressor, a condenser, a liquid refrigerant receiver and an evaporator together with suction conduit connection from the evaporator to the low side of the compressor and other means for connecting the high side of the compressor through the condenser and receiver to the evaporator including a liquid conduit line and control valve means, a defrosting system therefor comprising a secondary evaporator means connected to receive liquid refrigerant from the receiver of the refrigeration system, means for supplying controlled heat to be absorbed by the secondary evaporator, control valve means controlling flow of said liquid to the secondary evaporator, valve means for disconnecting the refrigeration evaporator from the low side of the compressor and connecting said secondary evaporator therewith so as to supply heat laden vapor thereto and for connecting the high side of the compressor directly to the refrigeration evaporator, and means for returning liquid from the refrigeration evaporator to the receive" in a manner by-passing the said control valve means of the ref'igcration system.

2. In combination with a refrigeration system having a compressor, a condenser, a liquid refrigerant receiver and an evaporator together with suction conduit connection from the evaporator to the low side of the compressor and other means for connecting the high side of the com, ressor through the condenser and receiver to the evaporator including a liquid line and control valve means, a. defrosting system therefor comprising a secondary evaporator means connected to receive liquid refrigerant from the receiver of the refrigeration system, means for supplying heat to be absorbed by the secondary evaporator, control means controlling flow of said liquid to toe seconoary evaporator, valve menus for disconnecting tte refrigeration evaporator from the low side of the com, =r and connecting said secondary evapo rzuor there-"i o to supply heat laden vapor thereto and for co. the high side of the compressor dily to the refriger 'on evaporator, means for returning uid from the refrigeration evaporator to the receiver in a manner lay-passing the said control valve means of the refri oration system, and means operable in response to a ecnd. at of the heat laden vapor from the secondary evaporator for controlling the amount of supplied heat for a rption by the secondary evaporator.

3. in comcination with a refrigeration system having a compressor, a co: denser, a liquid refrigerant receiver and an evaporator together with suction conduit connection from the evaporator to the low side of the cornpressor and other means for connecting the high side of the compressor through the condenser and receiver to the evaporator including a liquid line and control valve means. a defrosting system therefor comprising a secondary evaporator connected to receive liquid refrigerant from the receiver of the refrigeration system, means for supplying heat to be absorbed by the secondary evaporator, control valve means for controlling flow of said. liquid to the secondary evaporator, valve means for disconnecting the refrigeration evaporator from the low side of compressor and connecting said secondary evaporator therewith so as to supply heat laden vapor thereto and. for connecting the high side of the compressor directly to the refrigeration evaporator, means for returning liquid from the refrigeration evaporator to the receiver in a m nner ivy-par ing the control valve means of the refr :1 system, and means controlling the amount lied heat for absorption by the secondary dztion of the gaseous refrigerant generated by the secondary evaporator.

4. in combination with a refrigerating system having a compressor, a condenser. a liquid refrigerant receiver and an evaporator together with suction conduit connection from the evaporator to the low side of the compressor and other means for connecting the high side of the compressor through the condenser and receiver to the evaporator including a liquid conduit line and control valve means, a defrosting system therefor comprising a secondary evaporator means connected to receive liquid refrigerant from the receiver of the refrigeration system, means for supplying heat to be absorbed by the secondary evaporator including a body of fluid in heat exchange relation with the secondary evaporator, and means for changing the fluid, control valve means controlling {low of liquid to the s condary evaporator, valve means for disconnecting the refrigeration evaporator from the low side of the com pressor and connecting said secondary evaporator therewith so as to supply heat laden vapor thereto and for connecting the high side of the compressor directly to the refrigeration evaporator, means for returning liquid from the refrigeration evaporator to the receiver in a manner by-passing the said control valve means of the refrigeration system, and means including a regulating valve operable in response to suction pressure resulting from the absorption of heat by the secondary evaporator and the vaporization of liquid refrigerant for controlling the changing of the fluid in heat exchange relation with the secondary evaporator.

5. In a refrigeration system having a compressor with its low side normally connected to a refrigeration evaporator through a suction line and its high side normally connected to the evaporator through a liquid line, the combi nation therewith of means providing for reverse or eration of the system including a reversing valve for connecting the high side of the compressor to the evaporator through the suction line and the low side of the compressor to the evaporator through a water heated heat exchanger, said heat exchanger providing indirect heat exchange between the refrigerant and water therein, and means including valve means responsive to a condition of the gaseous refrigerant generated by the heat-exchanger for regulating replacement of the water in the heat exchanger to maintain the temperature of the water within a predetermined range during reverse operation of the system.

6. A hot gas defrosting system for refrigeration apparatus comprising, a secondary evaporator separate from the refrigeration system which functions during the refrigeration cycle, means for supplying heat to be absorbed by the secondary evaporator, a conduit between the secondary evaporator and the receiver of the refrigeration apparatus for supplying liquid refrigerant from the receiver to the evaporator, a conduit between the secondary evaporator and the low side of a compressor whose high side is connected to the evaporator to be defrosted, and means controlling flow of refrigerant through the secondary evaporator.

7. The system of claim 6 wherein means for supplying heat is controlled in response to changes in a variable condition of the gaseous refrigerant generated by the secondary evaporator.

8. The system of claim 6 wherein the means for supplying heat is a heat bearing liquid in indirect heat exchange relation with the refrigerant.

9. The system of claim 6 wherein the means for supplying heat is a heat bearing liquid circulated through the secondary evaporator in indirect heat exchange relation with the refrigerant, and valve means is provided for controlling the rate of flow of the heat bearing liquid in response to changes in a variable condition of the gaseous refrigerant generated by the secondary evaporator.

l0. The system of claim 9 wherein the valve means is responsive to changes in suction pressure of the system during the defrost cycle.

References Cited in the file of this patent UNITED STATES PATENTS 

